176 DEVELOPMENT OP THE WING-VENATION OF ODONATA, 



It is scarcely necessary now for me to say that these phylo- 

 genetic stages, taken from hying examples, do not lie along one 

 ahsolutely straight line of descent. Each, rather, lies a little off 

 the direct line that culminates in the Italian loop; nevertheless, 

 each is a true advance on the one hefore it. 



Stage 3. — Idocorduliini {Figs. 9 -10, and Plate xi., fig.6). We 

 now come to a stage exhibited by the rare larva of Austrocordulia 



A, Cu^ 



Fig.9. 



Fig. 10. 



Fig.9. — Ausfrocordnlia refracta Tillyard, cJ . Tracheation of full-grown 

 nymphal hindwing. (Stanwell Park, N.S. W.; Feb., 1914). 



Fig. 10. — Austrocordulia re/rac^a Tillyard, <5 . Portion of imaginal vena- 

 tion, to show structure of anal loop. (Heathcote, N.S. W.; from a 

 specimen, bred Dec. 20th, 1912). 



re/?-actoTillyard,( the only known larva of the tribe Idocorduliini) 

 which stands, in my opinion, very nearly in the direct line of 

 ascent to Stage 4. The line branched off from Stage 2 at a time 

 when the area between Ac and the triangle, though tending to 

 stretch more widely, was still only wide enough to support a loop 

 of two cells' width. At this point, a new force came into play, 

 viz., the beginning of a stretching transverse to the longitudinal 

 axis of the iving. The combination of forces started thaX diagonal 

 stretching which brought the Italian loop into being, and to which 

 the slantwise-elongated cells of the hindwings of almost all 

 Lihellulidce bear irrefutable witness. Not hy growth of new 

 ivi7ig -material , hut hy stretching out of the old, did this heautiful 

 formation arise. 



